Development of skeletal kinetics mechanisms for plasma-assisted combustion via principal component analysis

Abstract

The positive effect of plasma discharges on ignition and flame stability motivates the development of detailed kinetic mechanisms for high-fidelity simulations of plasma-assisted combustion. Because of their hierarchical nature, combustion processes require a large number of chemical species and pathways to describe hydrocarbon oxidation. In order to simulate kinetic enhancement by non-thermal electrons, additional species and processes are included, which model the ionization and excitation of neutral molecules. From a practical perspective, integrating large kinetics mechanisms is computationally burdensome due to the temporal stiffness of the nonlinear combustion dynamics and the memory requirements associated with the high number of species. In order to alleviate computational costs, a dimensionality reduction approach is proposed based on principal component analysis. The methodology is demonstrated on a detailed kinetics mechanism for plasma-assisted combustion excited by a nanosecond pulse discharge. Data are collected from a zero-dimensional twotemperature reactor model, whereby a nanosecond pulse generates a population of excited-state molecules and radicals in argon and air mixtures with hydrocarbon fuels. The data from the detailed mechanism are used to describe the evolution of the plasma and mixture based on principal components. Several skeletal mechanisms consisting of a much smaller number of species are assembled and their accuracy is compared against the detailed one. The performance of selected skeletal mechanisms is found satisfactory for the simulation of plasma-assisted ignition in unsteady, three-dimensional reactive flows.

A Machine-Learning Framework for Plasma-Assisted Combustion Using Principal Component Analysis and Gaussian Process Regression

“…First, the mechanism of 55 species will be reduced by relying solely on principal component analysis. This analysis is different from previous investigations where the original detailed mechanism of 163 species was reduced to 80 principal components [2]. In this work, we will start from the skeletal mechanism of 55 species, which already accounts for a major compression.…”

“…The objective is to represent the reaction kinetics using a reduced number of variables that reflect the behavior of the full system. Recent work has investigated various data-driven reduction techniques to obtain surrogate representations of the detailed plasma-assisted combustion physics ranging from graph-based techniques [3] to correlation-based techniques using principal component analysis [2]. A first class of techniques is given by the graph-based methods, such as the Directed Relation Graph method with Error Propagation (DRGEP) [9].…”

“…These components are a linear combination of the original variables and contain most of the variance in the system. In previous work on plasma-assisted combustion, the PCA-based model allowed reducing the number of variables by half from 163 species to 80 principal components without introducing any inaccuracies [2].…”

Combustion, Chemistry, and Carbon Neutrality

“…570,571,574 Current research in plasma-assisted combustion is devoted to study ignition, 575−580 flame stabilization and combustion enhancement, 578,581−586 kinetics and mechanism development, 575,579−581,587−590 process visualization, 576,577,582,591,592 species diagnostics, 575,582,584−586,588−590,593−597 electric field and/or electron density measurements, 586,596,598 and numerical simulation, 575,[577][578][579][580]584,591,592,597 using different types of plasma generation, e.g., with repetitively pulsed nanosecond, [576][577][578]581,585,586,[591][592][593]595,599 dielectric barrier discharge, 577,579,588,590,594,596,597 gliding arc, 582,583 and microwave 584 activation. Fuels include hydrogen, 577,597,…”

“…572 In addition to the concentrations of the main and intermediate combustion species, including excited and charged particles, the electric field and electron density distribution should be determined as a function of the fuel−oxidizer−bath gas system and of the relevant discharge parameters, on the time scales of the related processes. 570,571,574 Current research in plasma-assisted combustion is devoted to study ignition, 575−580 flame stabilization and combustion enhancement, 578,581−586 kinetics and mechanism development, 575,579−581,587−590 process visualization, 576,577,582,591,592 species diagnostics, 575,582,584−586,588−590,593−597 electric field and/or electron density measurements, 586,596,598 and numerical simulation, 575,[577][578][579][580]584,591,592,597 using different types of plasma generation, e.g., with repetitively pulsed nanosecond, [576][577][578]581,585,586,[591][592][593]595,599 dielectric barrier discharge, 577,579,588,590,594,596,597 gliding arc, …”